1. Field of the Invention
This invention related to optical measuring instruments and more particularly, to improvements in a ray beam converter having a rotary mirror for reflecting ray beams and converting the same into rotary scanning ray beams in an optical measuring instrument for measuring dimensions and the like of a workpiece to be measured by the utilization of the rotary scanning ray beams.
2. Description of the Prior Art
There have heretofore been optical measuring intruments, in which ray beams (laser beams) from a beam generator are reflected by a rotary mirror to be converted into rotary scanning ray beams, and dimensions and the like of a workpiece to be measured are measured by the utilization of the rotary scanning ray beams.
More specifically, as shown in FIG. 1, laser beam 12 are oscillated from a laser tube 10 (beam generator) toward a stationary mirror 14, the laser beam 12 thus reflected are converted into scanning ray beams 17 by a rotary mirror 16, the scanning ray beams 17 are converted into parallel scanning ray beams 20 by a collimator lens 18, a workpiece 24 to be measured interposed between the collimator lens 18 and a condensing lens 22 is scanned at high speed by the parallel scanning ray beams 20, and dimensions in the scanning direction (direction Y) of the workpiece 24 to be measured are measured from the time length of a dark portion or a bright portion generated due to the obstruction of the parallel scanning ray beams by the workpiece 24 to be measured.
The bright and dark portions of the parallel scannning ray beams 20 are detected as variations in input voltage of a light receiving element 26 disposed at the focal point of the condensing lens 22. Signals from the light receiving element 26 is fed to a pre-amplifier 28, where they are amplified (Refer to v), and then, fed to a segment (selector) circuit 30. This segment selector circuit 30 is adapted to generate a voltage V from the voltage outputted from the light receiving element 26 to open a gate circuit 32 only for a time t, during which the workpiece 24 to be measured is scanned, from the time of the voltage output of the light receiving element 26 and feeds the same to the gate circuit 32. A continuous clock pulses CP is fed to this gate circuit 32 from a clock pulse oscillator circuit 34, whereby the gate circuit 32 generates clock pulses P for counting the time t corresponding to a dimension in the scanning direction, for example, the outer diameter of the workpiece 24 to be measured and feeds the same to a counter circuit 36. Upon counting the clock pulses P, the counter circuit 36 feeds a count signal to a digital indicator 38, where the dimension in the scanning direction, i.e., the outer diameter of the workpiece 24 to be measured is digitally indicated.
In FIG. 1, designated at reference numeral 40 is a synchronous sine wave oscillator circuit, 42 a power amplifier and 44 a synchronous motor. The synchronous motor 44 rotates the rotary mirror 16 in synchronism with the clock pulses in response to synchronous signals fed from the synchronous sine wave oscillator circuit 40 in response to the continuous clock pulses CP fed from the clock pulse oscillator circuit 34, whereby the measuring accuracy is maintained.
The above described measuring method and device have been widely utilized because the lengths, thickness and the like of moving workpieces and workpieces heated to a high temperature can be measured at high accuracies in non-contact relationship therewith.
The aforesaid polygonal rotary mirror 16 in the optical measuring instrument of the type described is secured to a rotary shaft of a synchronous motor 44, however, in general, an eccentricity of the rotary mirror 16 at the time of being secured to the synchronous motor 44 and an inclination of the center axis of the configuration of the rotary mirror 16 relative to the rotary center axis of the motor and the like are not avoidable. Owing to those disadvantages, it has been inevitable that the rotary scanning ray beams 17 reflected by the rotary mirror 16 are disturbed to a certain extent.
Furthermore, eccentric rotation may occur in the rotor itself of the synchronous motor 44, and turbulences of the rotary scanning ray beams 17, and in its turn, of the parallel scanning ray beams 20 due to the eccentric rotation have been unavoidable.
Further, the aforesaid polygonal rotary mirror 16 has been ground and polished into a polygonal shape from a block of optical glass, and subjected to works such as vacuum-deposition onto the surfaces thereof with metal films, whereby the product is heavy in weight, reflecting surfaces composing respective surfaces of a polygon should be formed concentrical with the rotary center axis and in directions tangential to the rotating circle, and it is difficult to polish accurately, thus resulting in highly increased manufacturing cost.
Additionally, normally, a hexagonal shape and octagonal shape are used as the polygonal shape for the rotary mirror. The more the number of surfaces is, the more difficult the manufacture is and the lower the accuracy becomes. Further, a distance between the rotary surface of the rotary mirror 16 and the collimator lens 18 is periodically fluctuated in accordance with the rotation of the rotary mirror 16, whereby the parallel scanning ray beams 20, should necessarily be disturbed, to thereby cause a measuring error to a certain extent. However, the polygonal surfaces of the rotary mirror 16 cannot be polished accurately, thus presenting the disadvantage that the measuring error is further increased due to the insufficient polishing.